1. Field of the Invention
The present invention relates to the field of impellers for centrifugal compressors, and particularly to an impeller having novel placement of splitter blades.
2. Description of the Prior Art:
Centrifugal compressors have a wide ranging variety of applications, including typical use in superchargers or gas turbines. It is desirable to obtain a maximum efficiency for such compressors, particularly in relationship to particular ranges of operation. It is also important to obtain superior operating characteristics while retaining a compact design.
There are several design constraints in trying to optimize the operating characteristics of a centrifugal compressor. Various approaches have been pursued in the prior art to improve on compressor design, many of these relating to the blading of the impeller. However, the success of different blading approaches is difficult to predict, due to the unique nature of compressible fluids, as opposed to non-compressible fluids. For example, experience with centrifugal pumps used with incompressible liquids is not directly transferable to the design of compressors. For this and other reasons, many different types of designs have been proposed in the prior art, not all with great success.
In U.S. Pat. No. 4,167,369, issued to Ishihara on Sept. 11, 1979, there is described an impeller having specially contoured blades for use in a centrifugal compressor. The blades of the Ishihara design have an impeller portion extending radially of the impeller disk to its outer perimeter, and a centrally located inducer portion angled from the impeller portion in the direction of impeller rotation. The angle between the impeller portion and the front face of the disk is about 90 degrees at the inner end and gradually increases toward the outer end to about 50 to 70 degrees. Intermediate splitter blades are spaced equally between adjacent full blades. A dual entry centrifugal compressor is disclosed in U.S. Pat. No. 4,530,639 issued to Mowell on July 23, 1985, and includes splitter blades which are equally spaced between adjacent full blades.
In U.S. Pat. No. 4,060,337 issued to Bell, III on Nov. 29, 1977, there is described a centrifugal compressor having a splitter shroud in the flow path. The impeller of the Bell, III Patent includes blades which are all of identical height and contour. A centrifugal fan having associated pairs of blades of similar design is described in U.S. Pat. No. 2,083,996 issued to Jonn on June 15, 1937.
An offset centrifugal compressor is described in U.S. Pat. No. 4,615,659 issued to Sydransky on Oct. 7, 1986. The impeller of the Sydransky device includes blades which are comprised of three separate segments extending generally end-to-end. Gaps are provided between the adjacent ends of the blade parts to permit gas to travel therethrough from the Pressure side to the suction side, which is intended to control boundary layer build-up and reduce separation of gas from the blades.